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3 July 2012, Apache Lucene‚ 4.0-alpha available
The Lucene PMC is pleased to announce the release of Apache Lucene 4.0-alpha
Apache Lucene is a high-performance, full-featured text search engine
library written entirely in Java. It is a technology suitable for nearly
any application that requires full-text search, especially cross-platform.
This release contains numerous bug fixes, optimizations, and
improvements, some of which are highlighted below. The release
is available for immediate download at:
http://lucene.apache.org/core/mirrors-core-latest-redir.html?ver=4.0a
See the CHANGES.txt file included with the release for a full list of
details.
Lucene 4.0-alpha Release Highlights:
* The index formats for terms, postings lists, stored fields, term
vectors, etc
are pluggable via the Codec api. You can select from the provided
implementations or customize the index format with your own Codec
to meet your needs.
* Similarity has been decoupled from the vector space model (TF/IDF).
Additional models
such as BM25, Divergence from Randomness, Language Models, and
Information-based models
are provided (see
http://www.lucidimagination.com/blog/2011/09/12/flexible-ranking-in-lucene-4).
* Added support for per-document values (DocValues). DocValues can be
used for custom
scoring factors (accessible via Similarity), for pre-sorted Sort
values, and more.
* When indexing via multiple threads, each IndexWriter thread now
flushes its own segment
to disk concurrently, resulting in substantial performance improvements
(see http://blog.mikemccandless.com/2011/05/265-indexing-speedup-with-lucenes.html).
* Per-document normalization factors ("norms") are no longer limited
to a single byte.
Similarity implementations can use any DocValues type to store norms.
* Added index statistics such as the number of tokens for a term or
field, number of postings
for a field, and number of documents with a posting for a field:
these support additional
scoring models (see
http://blog.mikemccandless.com/2012/03/new-index-statistics-in-lucene-40.html).
* Implemented a new default term dictionary/index (BlockTree) that
indexes shared prefixes
instead of every n'th term. This is not only more time- and space-
efficient, but can
also sometimes avoid going to disk at all for terms that do not
exist. Alternative term
dictionary implementions are provided and pluggable via the Codec api.
* Indexed terms are no longer UTF-16 char sequences, instead terms
can be any binary
value encoded as byte arrays. By default, text terms are now encoded as UTF-8
bytes. Sort order of terms is now defined by their binary value,
which is identical
to UTF-8 sort order.
* Substantially faster performance when using a Filter during searching.
* File-system based directories can rate-limit the IO (MB/sec) of merge
threads, to reduce IO contention between merging and searching threads.
* Added a number of alternative Codecs and components for different
use-cases: "Appending"
works with append-only filesystems (such as Hadoop DFS), "Memory"
writes the entire
terms+postings as an FST read into RAM (see
http://blog.mikemccandless.com/2011/06/primary-key-lookups-are-28x-faster-with.html),
"Pulsing" inlines the postings for low-frequency terms into the
term dictionary (see
http://blog.mikemccandless.com/2010/06/lucenes-pulsingcodec-on-primary-key.html),
"SimpleText" writes all files in plain-text for easy
debugging/transparency (see
http://blog.mikemccandless.com/2010/10/lucenes-simpletext-codec.html),
among others.
* Term offsets can be optionally encoded into the postings lists and
can be retrieved
per-position.
* A new AutomatonQuery returns all documents containing any term
matching a provided
finite-state automaton (see
http://www.slideshare.net/otisg/finite-state-queries-in-lucene).
* FuzzyQuery is 100-200 times faster than in past releases (see
http://blog.mikemccandless.com/2011/03/lucenes-fuzzyquery-is-100-times-faster.html).
* A new spell checker, DirectSpellChecker, finds possible corrections
directly against the
main search index without requiring a separate index.
* Various in-memory data structures such as the term dictionary and
FieldCache are represented
more efficiently with less object overhead (see
http://blog.mikemccandless.com/2010/07/lucenes-ram-usage-for-searching.html).
* All search logic is now required to work per segment, IndexReader
was therefore refactored to
differentiate between atomic and composite readers
(see http://blog.thetaphi.de/2012/02/is-your-indexreader-atomic-major.html).
* Lucene 4.0 provides a modular API, consolidating components such as
Analyzers and Queries
that were previously scattered across Lucene core, contrib, and
Solr. These modules also
include additional functionality such as UIMA analyzer integration
and a completely reworked
spatial search implementation.
Please read CHANGES.txt and MIGRATE.txt for a full list of new
features and notes on upgrading.
Particularly, the new apis are not compatible with previous version of
Lucene, however, file
format backwards compatibility is provided for indexes from the 3.0 series.
This is an alpha release for early adopters. The guarantee for this
alpha release is that the index
format will be the 4.0 index format, supported through the 5.x series
of Apache Lucene, unless there
is a critical bug (e.g. that would cause index corruption) that would
prevent this.
Please report any feedback to the mailing lists
(http://lucene.apache.org/core/discussion.html)
Happy searching,
Apache Lucene/Solr Developers